Typically, a disk drive comprises one or more magnetic disks having magnetic surfaces for data storage. The disks are mounted on a spindle and continually rotated at a substantially constant speed. A plurality of head arm assemblies are arranged together in a stacked assembly resembling a comb-type structure. The main body of the HSA is an electromagnetic actuator which is controlled by a head positioning system. The actuator positions the magnetic heads or transducers to preselected concentric recording tracks under the control of an address signal supplied to the actuator from a data processing system.
Each transducer, or head, glides over the disk surface by a film of air created by the disk as it is rotated. This type of head as designated by numeral 101 in FIG. 1 is classified as “an air bearing head” and is attached to a flexible sheet metal member 102 by means of a gimbal type mounting. The pre-formed sheet metal, which is called load beam, is made of stainless steel and is connected to a nut plate 103 with laser welds. A combination of “load beam”, “gimbal type structure” and “air bearing head” is called Head Gimbal Assembly (HGA) 1. The HGA 1 is swaged to an actuator 2 comprising a body 201 on which a bearing 204 is mounted, a voice coil 202 arranged between two legs 205 of the body 201 and a number of arm fingers 203 extending from the body (FIGS. 2A and 2B). The head 101 is allowed to be biased toward the magnetic surface of the rotating disk for accessing the stored data.
The transducer is supplied with data signals during the recording mode of the disk drive. During reading of the recorded data, the transducer senses the magnetic transitions recorded on the disk representing the data. Each disk surface is associated with one HGA which, after being stacked up onto the actuator, forms a comb-type structure having the transducers at the distal ends of the HGAs with accurate vertical alignment. The complete assembly of HGAs with an actuator is called an HSA 3 (FIG. 2B) which is controlled to move over a corresponding path inside the hard disk drive.
In addition, the individual components on the HGA become more fragile and are easily damaged if extreme care is not exercised during each of the assembly operations. A head arm assembly operation generally comprises joining together a relatively stiff element and a relatively flexible element by a swaging operation. A head gimbal assembly (HGA) 1 comprises a magnetic transducer and a grimbal type mount attached to the distal end of the flexible element, usually by spot welding. The other end of the flexible element has a nut plate welded to the stiff element. The nut plate includes a cylindrical boss which extends normal to the flat surface of the plate and is designed to mate with an opening disposed in the end section of the rigid element. The elements are aligned precisely and spot welded to maintain their alignment during the subsequent swaging operation. The swaging operation as shown in FIG. 3 involves a series of steps in which a ball 32 slightly larger than the opening in a cylindrical boss 31 (not precisely scaled) is forced through the boss 31 thereby cold forming the boss material to the area of the rigid element surrounding the boss. This swaging operation has become the most critical step in the manufacturing process as the size of the components has decreased and their fragility has increased. The biasing force for the magnetic transducer is provided in the flexible elements by bending the flexible element along a line perpendicular to the lengthwise axis of the arm and subsequently returning the element to its original position while simultaneously stress relieving the bend area by heating it with a laser until the desired gram load force is obtained. The required gram load is determined by the flying characteristics of the transducer relative to the magnetic surface.
Assembly operations of the HSA involve providing a guide means, such as a guide hole, in the actuator end of the head arm. Each HGA is sequentially placed on a shaft with suitable ring type spacers between each arm. Each arm is affixed to the shaft by ball swaging or adhesive.
The HSA is provided with a shipping comb which functions to maintain the adjacent head arms spaced apart a predetermined distance while the HSA is being tested before installation in the disk drive. The shipping comb is arranged to pivot out of position during the gram load measuring operation to permit each head to apply a force to a sensing device that measures and displays the value of the gram load of that head to the operator.
After positioning the HSA on a platform, the operator moves the platform to the measurement position. The heads are measured one at a time. For example, where the HSA includes four heads, four separate sensing devices are provided so that the operator is advised if any head is out of specification.
With the decrease in size, the head arms become less sturdy and hence are more sensitive to the swaging operation with the result that the alignment of the heads may be adversely affected. Further, if an HGA arm proves, on testing of the head stack, to be out of specification for the gram load, the possibility of manually adjusting the flexible element to obtain the correct biasing force is almost impossible.
The rework operation to replace the HGA having the incorrect gram load with a new head, or to at least salvage the good head arms, (usually 3 arms) was very complicated due to the swaging construction and the more fragile nature of the smaller components.
A conventional HSA assembly process in which quasi-static testing (QST) can only be done after swaging and the rework process always requires de-swaging when HGA needs to be removed. This type of rework process is always time consuming, deforms the actuator, creates tremendous amount of particles and damages other quality HGA as well.
In order to overcome these problems, an HGA out of specification has to be identified before being swaged tightly to the actuator. It means that QST has done preferably before swaging so that the HGA out of specification can be replaced without going through the de-swaging process.
Consequently, a universal fixture is needed to hold HGAs in place while an HSA is being processed through various assembling and testing operations.